1. Field of the Invention
The present invention relates to devices and methods for making semiconductor devices, and in particular to a device and method for making monolithic bypass-diodes and solar cell string assemblies.
2. Description of the Related Art
Solar cells are used in various technologies to provide power to other electronic assemblies. Satellites, calculators, and power systems are all examples of solar cell usage.
A solar cell is a p-n junction created over a large area on a semiconductor substrate. The junction creates a voltage and current when light of certain wavelengths strike the surface of the solar cell, and, as such, solar cells are photovoltaic devices. These photovoltaic cells provide a lightweight, maintenance-free power source for various applications, and also provide a pollution-free, distributed energy generation source for use in power delivery systems.
Solar cells are typically long-life devices, but can have their efficiency reduced or destroyed by reverse biasing of the solar cell junction. To prevent this type of damage, bypass diodes (BDs) are used to allow current to flow in an anti-parallel direction to the current flow through the solar cell junction.
Bypass diodes are typically formed using an isolated island structure on the front surface of the solar cell, or are discrete parts that are not integrated with the solar cell. As such, these island structures or discrete devices are typically connected to the solar cell using additional wiring and/or additional metallization on the solar cell substrate. The use of additional wiring and/or additional metallization creates new failure points for solar cells, as well as adding to the weight and complexity of the solar cell structure. Additional weight and failure mechanisms are unacceptable in a spacecraft environment, because of the extreme additional costs involved. Further, additional metallization obscures the solar cell from receiving incident light, which reduces the efficiency of the solar cell structure.
Further, by placing the bypass diode on the front surface of the solar cell, the solar cell area is reduced, and, as such, the solar cell cannot generate as much power. Since the area of a solar cell is a primary design consideration in many applications, additional solar cells would be needed to generate the desired power, which would increase the area and weight of the cells used for a given application, which may prove unacceptable from a design standpoint.
It can be seen that there is a need in the art for a solar cell that has an integrated bypass diode. It can also be seen that there is a need in the art for a solar cell that has a bypass diode that allows for maximum solar cell area. It can also be seen that there is a need in the art for a bypass diode that minimizes the weight and failure points for solar cell devices.